Jenna and Sam sold a piece of property for $300,000, claiming that their basis was $150,000 and report a taxable gain of $150,000. Their 2016 return filed in February 2017 reported gross income of $250,000. Jenna and Sam later determine that the property's basis was actually $50,000, not $150,000, resulting in a $100,000 understatement of income on the 2016 return. The statute of limitations period in which the IRS may assess additional tax in this situation expires on April 15 of what year:

a. 2019

b. 2020

c. 2023

d. There is no expiration date for the statute of limitations in this context.